In some email I received from Marc, sie wrote:
> 
> I have a firewall with three working NICs. One hooks into a cable
> modem. One into ADSL. The third into my local network.
> 
> Problem: Cable and ADSL both try to convince my dhclient that they are
> the default route.
> 
> Details: Cable has more bandwidth, but ADSL is a good backup. I don't
> want to be forced to use two more machines just to do outgoing and
> incoming (via DNS round-robin at first) load balancing.
> 
> Has anyone else done this without completely re-writing the
> dhclient-script and doing clever sneaky custom code-type things?
> 
> Any hints? Pointers to other projects? Rotten vegetables for bringing
> up a regularly hashed topic?
> 
> I would be a perfect guinea pig to help you test ideas--not only do I
> have the ability to actually read and understand code (even C!), but
> I'm a nice guy with practically limitless patience to boot! :)
> 
> Thank you for any help. When we're done I'll be the one to write the
> FAQ and save you the trouble.

search the ipfilter mailing list archive.

there are people out there who use modem/cable to do this but I think it
is getting harder for ipf to allow it.